Q2 RC 110 Ch 5

Introduction to Blood Gas Assessments

• Blood gas assessments (ABGs) are crucial for respiratory therapists to monitor.

• An ABG measures gases within the blood, specifically PO2 (partial pressure of arterial oxygen) and PCO2 (partial pressure of arterial carbon dioxide).

• Evaluates blood acidity (pH) and bicarbonate (HCO3-) levels, which help balance blood pH.

Importance of Key Terms

• Understanding key terms is essential for effective communication and comprehension in blood gas assessment.

• This lecture serves as an introduction; further in-depth knowledge will be covered in Professor Chia's class.

Normal Values for Blood Gases

• Normal Values (Table 5.1, Page 71):

  • pH: 7.35 - 7.45 (arterial), 7.30 - 7.40 (venous)

  • PCO2: 35 - 45 mmHg

  • HCO3-: 22 - 28 mEq/L

  • PO2: 80 - 100 mmHg

• Knowing normal values is vital for identifying abnormalities.

Procedures for Blood Gas Collection

• Arterial Blood Gases (ABGs):

  • More invasive and painful, requiring a needle to access an artery.

  • considered the gold standard for accuracy in blood gas measurements.

• Venous Blood Gases (VBGs):

  • Easier to collect from an IV but less accurate than ABGs.

Acid-Base Relationships

• Acid-base abnormalities reflect respiratory conditions affecting ABGs.

• Key relationship: PCO2, bicarbonate, and pH interact to maintain blood homeostasis.

• Effects of PCO2 Changes:

  • Increase in PCO2 results in decreased pH (more acidic); occurs due to conditions like COPD or asthma.

  • Decrease in PCO2 leads to increased pH (more alkaline); often seen in neurological damage causing rapid breathing.

Compensation Mechanisms

• In response to acid-base imbalances, the body attempts to compensate:

  • The respiratory system adjusts ventilation to change CO2 levels.

  • Kidneys produce bicarbonate for long-term compensation, but this process is slow (days to weeks).

Understanding Blood Gas Values

• Ideal blood gas value: pH of 7.40, PCO2 of 40, HCO3- of 24.

• For every 10 mmHg increase in PCO2, pH decreases approximately 0.06 units.

• For example, a PCO2 of 50 results in a pH of about 7.34 due to increased acidity.

Common Acid-Base Abnormalities

• Acute Respiratory Alkalosis (Hyperventilation):

  • Caused by hyperventilation leading to decreased CO2, pH > 7.45, PCO2 < 35.

• Acute Respiratory Acidosis (Hypoventilation):

  • Caused by inadequate ventilation resulting in increased CO2, leading to decreased pH.

• Chronic Respiratory Acidosis:

  • Over time, kidneys compensate by producing more bicarbonate, maintaining a normal pH despite elevated CO2.

Metabolic Disorders and Their Effects

• Metabolic Alkalosis:

  • Involves an increase in bicarbonate, leading to a higher pH, unrelated to respiratory failure.

• Metabolic Acidosis:

  • Low pH due to insufficient bicarbonate; often caused by lactic acid buildup, renal failure, or diabetic ketoacidosis.

Common Errors in ABG Analysis

• Pre-analytic errors: Issues before sample analysis, such as problems with machines or collection equipment.

• Analytic errors: Issues during analysis, like picking up venous blood or sample exposure that alters results.

Conclusion

• Review and understand normal blood gas values, pH, CO2, and bicarbonate levels.

• Evaluating these values aids in identifying whether the blood is normal, acidic, or alkaline.

• Immediate review of literature and tables for severity classifications (normal: 80-100, mild: 60-80, moderate: 40-60, severe: <40 PO2) is recommended.

• Mastering this information is critical for effective assessment and decision-making in respiratory care.